Mantle upwellings above slab graveyards linked to the global geoid lows

Abstract

Supplementary Figure S1. Details of velocity structure for models S20RTS 1 (first column) and SB4L18 2 (second column), and model TX2005 3 (third column) in the zones of geoid minima. (a) Integrated tomography in depth range 2050-2850 km; (b) Integrated tomography in depth range 300-1000 km; (c) Cross section from North America to Ross Sea; (d) Cross section from central Asia to Ross Sea; (e) Correlation coefficient between 18 observed geoid and tomography calculated at every 100 km depth; (f) Observed geoid. Semi-transparent outlines on (a-b) cover zone of global geoid high; blue and red dashed lines (c-d) indicate lower mantle high velocity and upper-to-mid mantle low velocity 21 anomalies of interest, respectively; black, blue and red lines on (e) show mean correlation 22 coefficient between whole geoid, areas of negative geoid and areas of positive geoid, respectively; red lines on (f) indicate position of great circle cross-sections intersecting geoid low. Correlation coefficient between observed geoid and tomography models (e) is calculated as a product of values divided by product of standard deviations at every 100 km depth. The mean value of correlation coefficient is than calculated for whole geoid, areas of geoid lows, and geoid highs. 28 Integrated tomography plots (a-b) show a correlation between geoid low (f) and both 30 seismically fast regions in lower mantle (a) and slow regions in upper-to-mid mantle (b) for all investigated tomography models. In the region of NE Pacific geoid low, all models define a seismically fast anomaly in the lower 500-1000 km of mantle (c), which is 33 probably related to an ancient subducted slab that hasn't been recognized previously, 34 except by analysis of SKS-SKKS splitting discrepancies 4. A zone of upper-mid mantle 35 seismically slow velocities is located above this fast anomaly (c), model SB4L18 2 defines 2 nature geoscience | www.nature.com/naturegeoscience

The solid Earth's influence on sea level

“…This mantle water directly infl uences mantle dynamics, and thus sea level as well via dynamic topography or subduction initiation, by decreasing mantle viscosity (Hirth and Kohlstedt, 1996). Indeed, some mantle upwellings may be arising from regions of elevated water content above ancient subducted slabs (Spasojevic et al, 2010;van der Lee et al, 2008). Water from mantle rocks is released into the surface environment by degassing at mid-ocean ridges (Jambon and Zimmermann, 1990;Ligi et al, 2005;Michael, 1995;Shaw et al, 2010) and is replenished by subduction of hydrated minerals (Faccenda et al, 2012;Hacker, 2008;Jarrard, 2003;Rüpke et al, 2004;Savage, 2012;Shaw et al, 2008;van Keken et al, 2011).…”

Mantle updrafts and mechanisms of oceanic volcanism

“…Studies that include surface waves and types of data other than near-vertical relative travel times do not produce plume-like or deep slab-like features (4, 18, and references therein). Are the relatively low-velocity regions in the vicinity of Tonga-Fiji-Samoa produced by warmer material buoyantly rising from the deep mantle (a mantle plume) or are they passive updrafts, consequences of displacement of mantle material by, or volatile release from, the Pacific slab (32) at this location where the plate-arc convergence rate is highest in the world (33,34)? The Samoan islands and other "hotspot tracks" are close to but not centered on the inferred updrafts (2, 4, 31).…”

How subduction broke up Pangaea with implications for the supercontinent cycle

“…Geodynamic models have shown that subducted lithosphere can accumulate in the transition zone at the base of the upper mantle (Chen & Brudzinski 2001;Hamilton 2007), or at the base of the lower mantle just above the core-mantle boundary (Kendall & Silver 1996;Spasojevic et al 2010;Sutherland et al 2010;Tackley 2011). Accumulations of subducted lithosphere at the base of the upper mantle can start to sink rapidly into the deeper mantle in so-called slab avalanche events (Condie 1998;Pysklywec et al 2003;Capitanio et al 2009).…”